Tobacco dust is a by-product of tobacco processing and generally comprises minute tobacco particles created by tobacco breakage wherever tobacco is dropped, rolled, rubbed, tumbled, or impinged. Extremely fine tobacco dust is produced at leaf stemmery plants, whose dust has had so little utility in the trade that it has earned the nickname "stemmery discard".
Generally, practices have arisen to employ tobacco dust in conjunction with other tobacco-products, such as stem pieces and leaf scraps in the preparation of a reconstituted tobacco material. Heretofore, these practices did not operate well with stemmery discard.
A known process for making reconstituted tobacco sheet includes grinding tobacco stem together with a portion of tobacco dust; placing the mixture in a solution of diammonium phosphate (DAP) and ammonia; holding the solution in a tank for several hours until the diammonium phosphate and ammonia chemically release the natural pectins from the tobacco particles; and casting the resultant slurry onto a moving belt. The released pectins chemically bind the tobacco particles as the cast slurry is dried and then cut. This type of process may suffer difficulties if the original tobacco feed stock does not include a substantial portion of tobacco particles ladened with natural pectins. Some forms of tobacco fines from stemmery discard may be deficient in this regard when attempted with this type of (DAP) process.
The inclusion of DAP in the process of making this form of reconstituted tobacco creates a characteristic subjective note to this product. Also, interest has arisen to produce reconstituted sheet with as few added ingredients as possible, and this process is not operative without the addition of DAP.
A second type of process incorporates paper making techniques in the construction reconstituted tobacco sheet. The process begins with the extraction of soluble fractions of incoming tobacco feed stock and forming the insoluble products (comprising mostly fiber) into a slurry for production of a base-web in accordance with paper making practices. At the same time, the soluble fractions are concentrated and recombined with the base-web to form a final coated sheet. This process requires a high percentage content of stemmed particles in the composition so as to achieve sufficient fiber content for the paper making portion of the process. Extremely fine tobacco particles in the tobacco stock is problematic in that it readily passes through the fourdrinier wire and oftentimes finds its way into the white-water of the paper making facility.
Yet another genre of processes for constructing reconstituted tobacco sheet material includes those which attempt sheet construction by the addition of a binder material in solution with finely ground tobacco. Such processes are disclosed U.S. Pat. No. 2,769,734 to Bandel. In Bandel, tobacco is dry ground and then commingled with a preparation of water and adhesive, whereupon the tobacco is extruded onto an endless moving surface, dried and rolled into tobacco sheet. The process in Bandel is primarily directed to forming a self supporting tobacco sheet such as a cigar wrapper which preferably includes a film forming agent. The examples provided in the patent to Bandel include a portion of wood pulp fiber. The presence of wood pulp in the construction of reconstituted sheet can render a "papery" note to its smoke.
Tobacco sheet constructed from the DAP process provide a just adequate tensile strength of approximately 15 kilograms per meter. Tobacco sheet constructed from the paper-making technique has improved tensile strength of about 50 kilograms per meter, but such is dependent upon the inclusion of fiber in the laid slurry and is not workable with a 100% tobacco dust content sheet strength is an important parameter, because the stronger sheet will provide statistically longer strand lengths and will suffer less breakage (and less re-creation of dust).